Fuel element for nuclear reactor



y 1951 J. s. HOLLINGS 2,985,576

FUEL ELEMENT FOR NUCLEAR REACTOR Filed Nov. 26, 1956 United StatesPatent '0 M 2,985,576 FUEL ELEMENT'FOR NUCLEAR REACTOR John ShawHollings, Derby, England, assignor to Rolls- Royce Limited, Derby,England, a British company This inventioncomprises improvements in orrelating to nuclear reactors and has for an object to provide animproved fuel element for such reactors.

According tothe present invention, a fuel element for a nuclear reactorcomprises a thin sheet formed from clad uranium and arranged in aplurality of layers which are held in spaced relation to affordtherebetween flow paths for the cooling fluid of the reactor, thespacing of the layers being such as to obtain good heat transfer betweenthe fuel and the cooling fluid. The uranium may be clad for example inaluminium, steel, zirconium, niobium or beryllium.

Such a fuel element may be employed with especial advantage in agas-cooled, say helium-cooled, reactor.

According to'a preferred feature ofthis invention, the fuel element isformed by winding the sheet into a spiral whereof the convolutions orlayers are held in spacedrelation by rods inserted substantially axiallybetween the convolutions whereby cooling fluid flow paths are formedwhich extend axially of the fuel element.

According to another feature of this invention, there is provided a fuelunit comprising a tubular casing and a plurality of'such fuel elementsarranged end to end within the tubular casing which is adapted forinsertion in and withdrawal from the reactor core. Preferably in such anarrangement the fuel elements are provided with the ends of the sheet orsheets forming them in axiallyspaced relation. Al so the outer layer orlayers of the fuel elements are held in spaced'relation to the wall ofthe tubular casing to permit the cooling fluid to flow around theoutside of the elements as well as between the layers thereof.

One embodiment of the invention will now be described in detail withreference to the accompanying drawings in which:

Figure 1 shows a fuel element,

Figure 2 shows a fuel unit in position in a reactor,

Figure 3 is a section through the fuel element, and

Figure 4 is a detail.

The invention in this instance is applied to fuel elements forgraphite-moderated helium-cooled reactors.

The reactor may for instance comprise a core of graphite with a largenumber of fuel-unit-receiving parallel bores running through it, thebores being arranged in a triangular lattice pattern. The bores at oneend of the core open into a cooling gas supply chamber and at theopposite end of the core into a gas outlet chamber. The reactor alsoincludes a graphite reflector around the core and control elementsarranged for adjustment in the reflector to control the operation of thereactor.

Each bore is of such length as to accommodate a fuel unit between spiralgraphite elements disposed at each end of the bore, the spiral graphiteelements which in effect form part of the reflector, preventing neutronstreaming, whilst at the same time permitting passage of the coolinggas.

A fuel unit (Figure 2) comprises an open-ended cyaxial projections toabut adjacent fuel elementsto hold 5 lindrical metal tube 10 housing aplurality of fuel elements 11, say eight elements, arranged end to end.The tube 10 has a length somewhat greater than the total length of thefuel elements 11 and is indented circumferntially adjacent each end toprovide internal ribs 12 for retaining the fuel elements'll in position.The portions of the tube 10 beyond the ribs 12 are provided with holes13 to be engaged by the manipulating means by which the fuel unit ishandled.

The fuel elements are formed from sheet metal (Figure 4) which comprisesa core 14 formed by a sheet of enriched uranium, and a coating 15 ofaluminium, steel, beryllium, niobium, or zirconium alloy or the like oneach surface and around the edges of the uranium sheet. The coating 15prevents fission products entering the cooling gas. The sheet may forinstance be 0.022 inch thick including the coating which may be 0.003inch thick.

The sheet has a rod 16 of inert material brazed to it along one edge,and to its opposite edge there is brazed the edge of a flange 17aprojecting from the thicker part of a thin wedge-section plate 17 ofinert material, the flange being in effect a continuation of one surfaceof the wedge section.

The sheet is wound into a spiral form (Figures 1 and 2) using the rod 16as a core and so that the wedge-section plate 17 provides a portion at agreater radius than of the outer surface of the last of the convolutionsor layers 18 of the spiral, and spacer rods 19 of inert material arebrazed in position between the convolutions or layers 1 8 to maintainthem in spaced relation, say with a spacing of about ,5 inch. Also anumber of rods 20 are brazed to the external surface of the outermostconvolution or layer. The rods 16, 19, 20 extend parallel to the axis ofthe spiral coil. The arrangement is such that the space for cooling gasadjacent the whole of the uranium core of the sheet is of substantiallyuniform width.

The core rod 16, the rods 20. on the external surface of the outermostconvolution and the wedge-section piece :17 project beyond each end ofthe coil, and the wedgesection piece 17 has a notch 21 at one end and atongue 22 at the. other. All the fuel elements 11 are arranged to occupythe same angular position in the tube 10, the tongue 22 on a fuelelement engaging the notch21 in the next fuel element, and also thecoils of the fuel elements 11 are maintained in axialy-spaced relationin the tube by abutment of the projecting parts of the rods 16, 20 andwedge-section pieces 17.

In use, the cooling gas flows axially through the fuel unit passingthrough the spaces between the convolutions or layers 18 of the fuelelements 11 and also through the spaces between the extrenal surfaces ofthe fuel elements 11 and the internal surface of the tube 10, thussecuring good heat transfer from the fuel elements 11 to the coolinggas.

Fuel elements in accordance-with the invention are comparatively simpleto manufacture, and have a large surface area in contact with the heattransfer medium in relation to their weight.

Moreover, since the heat is actually produced in the thin spiral sheet,the efficiency of heat transfer from the fuel to the cooling medium ishigh.

I claim:

1. A fuel element for a nuclear reactor comprising a sheet of claduranium of spiral form, the spiral having several convolutions, one edgeof the sheet being at the center of the spiral and the opposite edge ofthe sheet being in the external surface of the spiral, a core rodrigidly secured to said one edge of the sheet and extending parallel tothe axis of the spiral, a plurality of axially-extending spacer rodsrigidly secured to the sheet be tween the convolutions of the spiralthereby to hold the convolutions in spaced relation, whereby coolingfluid of the reactor can flow between the convolutions of the spiral, aplurality of circumferentially-spaced rods extending axially of thespiral and secured to the external surface of the outermost convolutionof the spiral, said core rod and said circumferentially-spaced rodsproject'- ing axially beyond the ends of the spiral sheet, and a wedgesection piece secured to said opposite edge of the sheet and atfordingthe circumferential continuation of the outermost convolution of thespiral, said wedge section piece extending at its ends axially beyondthe ends of the spiral sheet, one'end of the wedge piece having a notchtherein and the opposite end having thereon an axially-projectingtongue.

2. A fuel unit for a nuclear reactor comprising a tubular casing and aplurality of fuel elements accommodated Within the tubular casing in endto end relationship, each of said fuel elements comprising a sheet ofclad uranium of spiral form, the spiral having several convolutions, oneedge of the sheet being at the center of the spiral and the oppositeedge of the sheet being in the external surface of the spiral, a corerod rigidly secured'to said one edge of the sheet and extending parallelto the axis of the spiral, a'plurality of axially-extending spacer rodsrigidly secured to the sheet between the convolutions of the spiralthereby'to hold the convolutions in spaced relation, whereby coolingfluid of the reactor can flow between the convolutions of the spiral, aplurality ofcircumferentially-spaced rods extending axially of thespiral and secured to'the external surface of theoutermostconvolution'of the'spiral, said core rod and saidcircumferentially-spaced rods projecting axially beyond the ends of thespiral sheet, and a Wedge section piece secured to said opposite edge ofthe sheet and affording a circumferential continuation of the outermostconvolution of the spiral, said Wedge se'cti'on piece extending at itsends axially beyond the ends of the V spiral sheet, one end of the wedgepiece having a notch therein and the opposite end having thereon anaxiallyprojecting tongue, the ends of the core rodand'circumferentially-spaced rods of each fuel element abutting thecorresponding rods of adjacent fuel elements to hold the fuel elementsin axially-spaced relation, and the tongue on the wedge piece of eachfuel element engaging the notch in the wedge piece of an adjacent fuelelement to hold the fuel elements angularly with respect to one another.

3. A fuel element for a nuclear reactor comprising a sheet of claduranium in spiral form, one edge of the sheet being at the center of thespiral and the spiral having several convolutions successively oneoutside the other, said convolutions being radially spaced apart, andspacer members extending axially of the spiral, disposed between theconvolutions and secured to the sheet to hold the convolutions inradially spaced relatiomsaid convolutions and spacer means definingaxially-extending flow paths between the convolutions,

4. A fuel unit for a nuclear reactor c'omprisin'g'a tubular casing and aplurality of fuel elements accommodated within the tubular casing in'end-to-end relationship, each of said fuel elements comprising a sheetof clad uranium in spiral form one edge of the sheet being at the centerof the spiral and the spiral having several convolutions successivelyone outside the other, said convolutions being radially 7 spaced apart,and spacer members extending axially of the spiral, disposed between theconvolutions, and secured to the sheet to hold the convolutions inradially spaced relation, said convolutions and spacer means definingaxiallyextendin'g flow paths between the convolutions, further spacermembers secured to the outermost convolution of the spiral and holdingthe outer-most convolution in radially spaced relation to the tubularcasing, and axially abutting parts project-ing axially from the fuelelements and i'nterabutting to hold the fuel elements in axially-spacedrelation.

References Cited in the tile of this" patent UNITED STATES PATENTS 713,913 Schmitz Feb. 27, 1906 2,780,596 Anderson Feb. 5, 1 957 2,313,073Saller et al. Nov. 12, 1957 2,831,806 Wigner Apr.22, 1958 2, 32,7 Wig erApi- 29, 9 2,879,216 Hurwitz et al. Mar. 24, 1959 FOREIGN PATENTS999,330 France July 16, 1952 OTHER REFERENCES Atomic Industry Reporter,News and Analysis, Number 9, Aug, 3, 1955,-Sec 1 -59.

Cunningham et al.: p/953, Proceedings of the Inerna- "tion-a1 Conferenceon the-Peaceful Uses of Atomic Energy, August 1955, vol. 9, pub. (I956)-by United Natio'ns, N.Y., pages 203--207.

1. A FUEL ELEMENT FOR A NUCLEAR REACTOR COMPRISING A SHEET OF CLADURANIUM OF SPIRAL FORM, THE SPIRAL HAVING SEVERAL CONVOLUTIONS, ONE EDGEOF THE SHEET BEING AT THE CENTER OF THE SPIRAL AND THE OPPOSITE EDGE OFTHE SHEET BEING IN THE EXTERNAL SURFACE OF THE SPRIAL, A CORE RODRIGIDLY SECURED TO SAID ONE EDGE OF THE SHEET AND EXTENDING PARALLEL TOTHE AXIS OF THE SPIRAL, A PLURLITY OF AXIALLY-EXTENDING SPACER RODSRIGIDLY SECURED TO THE SHEET BETWEEN THE CONVOLUTIONS OF THE SPIRALTHEREBY TO HOLD THE CONVOLUTIONS IN SPACED RELATION, WHEREBY COOLINGFLUID OF THE REACTOR CAN FLOW BETWEEN THE CONVOLUTIONS OF THE SPIRAL, APLURALITY OF CIRCUMFERENTIALLY-SPACED RODS EXTENDING AXIALLY OF THESPIRAL AND SECURED TO THE EXTERNAL SURFACE OF THE OUTERMOST CONVOLUTIONOF THE SPIRAL, SAID CORE ROD AND SAID CIRCUMFERENTIALLY-SPACED RODSPROJECTING AXIALLY BEYOND THE ENDS OF THE SPIRAL SHEET, AND A WEDGESECTION PIECE SECURED TO SAID OPPOSITE EDGE OF THE SHEET AND AFFORDINGTHE CIRCUMFERENTIAL CONTINUATION OF THE OUTERMOST CONVOLUTION OF THESPIRAL, SAID WEDGE SECTION PIECE EXTENDING AT ITS ENDS AXIALLY BEYONDTHE ENDS OF THE SPIRAL SHEET, ONE END OF THE WEDGE PIECE HAVING A NOTCHTHEREIN AND THE OPPOSITE END HAVING THEREON AN AXIALLY-PROJECTINGTONGUE.